Nielsen under-reported ratings for Allbritton’s ABC affiliate between May 2008 and March 2009. Citing a “procedural error,” the ratings giant failed to properly measure digital viewing.

Allbritton has a unique operation in Birmingham, with a pair of ABC affiliates on opposite sides of the DMA airing identical programming and being measured as WBMA+.

A Nielsen spokesperson said Allbritton’s non-traditional set-up in that DMA factored into the mistake. “Audience estimates for WBMA+ are to reflect tuning to WBMA and tuning to WCFT and WJSU, two full-powered satellite stations that distribute the analog and digital simulcast of WMBA’s signal,” the company said in a statement. “A procedural error caused the tuning to the digital simulcasts of WBMA by WCFT and WJSU (received via broadcast, cable or DBS distribution) not to be added to the three stations’ analog tuning between May 26, 2008 and March 23, 2009.”

WBMA+ President/General Manager Mike Murphy said ratings and shares were often less than half of what he would expect them to be. “Television stations are wholly dependent on accurate ratings from Nielsen,” he said. “When they get the numbers wrong, the stations are harmed, advertisers are harmed and viewers are harmed.”